1. Field of the Invention
The present invention relates to a rear wheel steering device and a method for rear wheel steering for a vehicle with a suspension member having a leaf spring.
2. Description of Related Art
Recently, Japanese Utility Model Laid-Open Publication No. 2-120284 (1990) discloses that a four wheel steering system or a device for steering rear wheels in accordance with front wheel steering has been provided in order to improve an operation stability while driving a vehicle at high speed.
In the above described conventional four wheel steering device, to rotate a rear axle housing around the center point when the rear wheels are steered, the rear axle housing is connected to one end of a bell crank rotatably supported by a leaf spring device. The other end of the bell crank is connected to a piston axis of a hydraulic cylinder device fixed at a differential case provided at the center point of the rear axle housing along a width direction of a chassis.
In the above rear wheel steering device, a rear wheel steering actuator, that is, a hydraulic cylinder device is supported by the rear axle housing which is shocked and displaced along a vertical direction while the vehicle is driven, so that the rear wheel steering device is apt to be damaged early. Thus, a durability of the rear wheel steering device and a reliability for the rear wheel steering device are insufficient.
One example of an actuator for steering rear wheels provided at a chassis is described in Japanese Patent Laid-Open Publication Nos. 62-194976 (1987) and 212109 (1988).
Japanese Patent Laid-Open Publication No. 62-194976 describes a structure in which a rear axle housing is frictionally slided on a leaf spring device and the size of rear wheel steering actuators is large. In this structure, durability of the structure is not enough and reliability for the structure is insufficient. Further, it is necessary to provide a pair of large sized rear wheel steering actuators, so that a weight of the structure becomes heavy and a pipe arrangement for the rear wheel steering actuators becomes complicated.
Japanese Patent Laid-Open Publication No. 63-212109 describes a structure in which a leaf spring device is movable along a longitudinal direction of a chassis. Under the structure, large and heavy leaf springs have to be moved along the longitudinal direction while rear wheels are steered. Also, a pair of left and right rear wheel actuators must be provided so that the rear wheel steering actuators have to become larger and heavy and a pipe arrangement for the rear wheel steering actuators becomes complicated. This structure makes it impossible to provide an economical four wheel steering system.